Emission Peculiarity
There are two nodes that can be used to generate a random number within your node group.

Object Info -&gt; Random generates a random number between 0 and 1 for each individual object.
Geometry -&gt; Random Per Island does the same for each disjointed piece of mesh within an object.  So this one can be used with Array modifier, for example.

You can use these random values for many purposes.  You can basically seed your textures by changing the position of the texture in coordinate space, or drive the W value of a 4d texture.  You can also use a color ramp to define a range of colors to choose from.

The Math -&gt; Multiply node can be used to effectively modify the range of the output.  E.g. multiplying by 20 gives you a random number between 0 and 20.